Light source optical system and projection display apparatus employing the same

ABSTRACT

A light source optical system includes a micro lens array, a condenser lens unit, and a dichroic surface. In a direction orthogonal to an optical axis in a cross section parallel to a normal of the dichroic surface and the optical axis of the condenser lens unit, a width of the dichroic surface is narrower than a width of the condenser lens unit. A light source optical system satisfies a predetermined conditional expression.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a light source optical system and aprojection display apparatus employing the same.

Description of the Related Art

In recent years, a projector has been developed that irradiates afluorescent body with a light flux emitted from high output laser diodes(hereinafter referred to LDs) as an excitation light, and includes awavelength-converted fluorescent light as a light source light. In sucha projector, the brightness of the projector can be increased byincreasing the number of LDs and/or increasing the output of each LD.

However, the light density of a light source spot formed on afluorescent body surface is increased when the strength of incidentlight onto the fluorescent body is increased to increase the brightness.As a result, a problem such as reduction of the light conversionefficiency occurs because of a luminance saturation phenomenon, andtherefore, the brightness proportional to the increase in the output ofthe LD cannot be obtained.

A technique discussed in United States Patent Application PublicationNo. 2012/0133904 is known as a technique to solve such a problem. UnitedStates Patent Application Publication No. 2012/0133904 discusses aconfiguration in which two fly-eye lenses are provided on the latterstage of an optical system for compressing light fluxes from a pluralityof LDs. Such a configuration can uniformize the light density of thelight source spot formed on the fluorescent body and suppress theoccurrence of an area having an extremely high light density to suppressthe reduction of the light conversion efficiency described above.

The configuration discussed in United States Patent ApplicationPublication No. 2012/0133904 requires not only the LD for exciting thefluorescent body but also an LD for guiding a blue color light to acolor separating and combining system and an optical system therearound,leading to increasing the entire apparatus size.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a technique forachieving a smaller light source optical system capable of suppressingthe reduction in the light conversion efficiency of the wavelengthconversion element and a projection display apparatus employing thesame.

A light source optical system configured to guide a light flux from alight source to a wavelength conversion element includes a first lenssurface array including a plurality of first lens surfaces, a secondlens surface array including a plurality of second lens surfaces andconfigured to receive a light flux from the first lens surface array, acondense optical system having a positive power configured to guide alight flux from the second lens surface array to the wavelengthconversion element, and a light guide surface configured to guide thelight flux from the second lens surface array to the wavelengthconversion element via the condense optical system, In a directionperpendicular to an optical axis of the condense optical system in across section parallel to a normal of the light guide surface andincluding the optical axis of the condense optical system, a width ofthe light guide surface is narrower than a width of the condense opticalsystem, and the following expression is satisfied:

$0.25 < {N \cdot S_{LA} \cdot {\frac{S_{LA}}{f_{LA}^{2}}\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}}$where the number of the second lens surfaces is defined as N, a focallength of the second lens surface is defined as f_(LA), and an area ofthe second lens surface is defined as S_(LA).

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a configuration of a light sourceapparatus according to a first exemplary embodiment of the presentinvention.

FIGS. 2A and 2B are diagrams each illustrating a configuration of adichroic mirror.

FIG. 3 is a diagram illustrating uniformization of a laser light flux bya lens array.

FIGS. 4A and 4B are graphs each illustrating a definition of a lightflux diameter.

FIGS. 5A and 5B are diagrams each illustrating a relationship between alens array and a light source image used in the first exemplaryembodiment of the present invention.

FIG. 6 is a diagram illustrating a change in an angle variation of alight flux caused by the light flux passing through an afocal system.

FIGS. 7A and 7B are diagrams illustrating a relationship between Fnumbers of an excitation light path and a fluorescent light path.

FIG. 8 is a diagram illustrating a configuration of a light sourceapparatus according to a second exemplary embodiment of the presentinvention.

FIG. 9 is a diagram illustrating a configuration of a projector on whicha light source apparatus according to each exemplary embodiment of thepresent invention can be mounted.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will be described belowwith reference to the drawings. However, relative arrangements and thelike of constituent components described in the exemplary embodimentsmay be changed as necessary according to the configurations and variousconditions of the apparatus to which this invention is to be applied.More specifically, the present invention is not limited to the exemplaryembodiments described below, and various modifications and changes canbe made within the scope of the gist of the present invention.

Hereinafter, a first exemplary embodiment of the present invention willbe described in detail with reference to the accompanying drawings.

(Configuration of Light Source Optical System and Light SourceApparatus)

FIG. 1 is a diagram illustrating a configuration of a light sourceapparatus as the first exemplary embodiment according to the presentinvention. In FIG. 1, a direction parallel to an optical axis of acondenser lens unit 8 described below is defined as an X axis direction,a direction in which a surface parallel to the X axis direction and tothe normal of a dichroic mirror 7 (described below) is an XZ crosssection is defined as a Z axis direction, and a direction perpendicularto the X axis direction and the Z axis direction is defined as a Y axisdirection. Accordingly, FIG. 1 is a diagram of the XZ cross section asindicated by the coordinate axes illustrated therein.

The light source apparatus according to the present exemplary embodimentincludes a light source 1, a collimator lens 2, a fluorescent body 9,and a light source optical system. The light source optical systemreferred to herein relates to a micro lens array 63, the dichroic mirror7 (light guide element), the condenser lens unit 8 (condense opticalsystem), and a light guide optical system. The light guide opticalsystem referrers to a parabola mirror array 3 including a plurality ofmirrors each having paraboloid having a curvature radius and a vertexcoordinate that are different from one another, flat mirrors 4, and aconcave lens 5.

(Light Path from Light Source 1 to Illumination Optical System)

The light source 1 is a laser diode (LD) emitting blue color light. Thelight flux emitted from the light source 1 is a diverged light flux, andas many collimator lenses 2 as the light sources 1 are provided in theadvancing direction of the light flux from the light source 1. Acollimator lens 2 is a positive lens making the diverged light flux fromthe light source 1 into a parallel light flux.

A plurality of light fluxes having been emitted from the collimatorlenses 2 advances in the Z axis direction, and thereafter, travels tothe flat mirrors 4 while the distances therebetween are reduced by theparabola mirror array 3. The light fluxes reflected by the flat mirrors4 are incident upon the concave lens 5. The concave lens 5 sharing itsfocal position with the focal point of the parabola mirror array 3 emitslight fluxes as parallel light fluxes.

The parallel light fluxes emitted from the concave lens 5 are incidentupon a first lens surface array 61 which is one of the surfaces of themicro lens array 63 and at the side of the concave lens 5, and areincident upon a second lens surface array 62 while being split into aplurality of light fluxes. More specifically, the second lens surfacearray 62 is provided at the position to receive the light fluxes fromthe first lens surface array 61.

The split light fluxes emitted from the second lens surface array 62 arereflected by the dichroic mirror 7 and travels to the condenser lensunit 8. The dichroic mirror 7 has the minimum size required forreflecting the light fluxes from the second lens surface array 62, andhas surface coated with a dielectric multilayered film (dichroic film)that reflects the blue color light from the light source 1 but allowslight having a fluorescent light wavelength (described below) totransmit therethrough.

(Configuration of Dichroic Mirror 7)

The detailed configuration of the dichroic mirror 7 is as illustrated inFIGS. 2A and 2B. The dichroic mirror 7 illustrated in FIG. 1 has theconfiguration of FIG. 2A. More specifically, the dichroic mirror 7 has aconfiguration in which transmission surfaces 72 transmitting any lightregardless of its wavelength are provided at the right and left in the yaxis direction of the dichroic surface 71, which is light guide surfacethat reflects the blue color light from the light source 1 and allowsthe fluorescent light including the green color light and the red colorlight to transmit therethrough.

It should be noted that the dichroic mirror 7 is not limited to theconfiguration as illustrated in FIG. 2A. For example, as illustrated inFIG. 2B, the dichroic mirror 7 may have such a configuration that thetransmission surface 72 is provided around the dichroic surface 71.Furthermore, at least one side of the dichroic surface 71 may beconfigured to overlap a certain side of the transmission surface 72, andthe transmission surface 72 may be either a surface on the transparentsubstrate, or an anti-reflection coated surface.

In a case where the normal of the dichroic surface 71 is not included inthe cross section parallel to the normal of the dichroic surface 71 andincluding the optical axis of the condenser lens unit 8, a width D_(d)(described below) just needs to be defined in a surface on which thedichroic surface 71 is projected vertically in this cross section.

The split light fluxes reflected by the dichroic mirror 7 are condensedand overlapped on the fluorescent body 9 by the condenser lens unit 8having a positive power. As a result, a light source spot is formed onthe fluorescent body 9. The light source spot formed on the fluorescentbody 9 is conjugate to each lens cell (lens surface) of the first lenssurface array 61, so that the light source spot has a rectangularuniform distribution.

(Configuration for Suppressing Reduction in Light Conversion Efficiencyof Fluorescent Body 9)

A description is given of the reason why the reduction in the lightconversion efficiency of the fluorescent body 9 can be suppressed byproviding the micro lens array 63 with reference to FIG. 3.

FIG. 3 is a diagram illustrating, in a simplified manner, an opticalrelationship of the first lens surface array 61, the second lens surfacearray 62, the condenser lens unit 8, and the fluorescent body 9 asillustrated in FIG. 1. The first lens surface array 61 corresponds to afirst lens surface array 61′, the second lens surface array 62corresponds to a second lens surface array 62′, the condenser lens unit8 corresponds to a condenser lens unit 8′, and the fluorescent body 9corresponds to a fluorescent body 9′.

The fluorescent body 9′ is positioned so as to become substantiallyconjugate to each lens cell of the first lens surface array 61′ with thesecond lens surface array 62′ and the condenser lens unit 8′. The firstlens surface array 61′ and the surface of the fluorescent body 9′ are inan image-forming relationship. Accordingly, a light source imagecorresponding to a light distribution formed on each lens cell of thefirst lens surface array 61′ is formed on the fluorescent body 9′. Thesize of the light source image is determined based on a pitch of a lenscell (a width of a lens cell) and a magnification of an image formingsystem. Furthermore, the light source image formed on each lens cell isdisposed to overlap with each other on the fluorescent body 9′ via thecondenser lens unit 8′.

As illustrated at the left side of FIG. 3, even in a case where thelight fluxes incident upon the first lens surface array 61′ have anon-uniform luminance distribution, the light distribution formed oneach lens cell is averaged according to the number of lens cells for theabove reason. As a result, a light source image having a uniformdistribution can be formed on the surface of the fluorescent body 9′ asillustrated at the right side of FIG. 3.

Referring back to explanation about FIG. 1, at the time when the lightfluxes made into parallel light by the concave lens 5 are incident uponthe first lens surface array 61, they make a discrete light distributionin which the light fluxes from the light sources 1 are separated fromeach other with an interval. However, through splitting and overlappingvia the above paths, a light source image having a uniform lightdistribution in a shape similar to each lens cell shape of the firstlens surface array 61 is formed on the fluorescent body 9. In thismanner, the light fluxes from the light sources 1 are less likely to beconcentrated on a single spot on the fluorescent body 9, and a reductionin the light emission efficiency due to luminance saturation phenomenoncan be suppressed.

(Configuration for Realizing Reduction in Size)

The blue color light emitted from the light source 1 and incident uponthe fluorescent body 9 is converted into a fluorescent light mainlyincluding a spectrum of red color light and green color light(conversion light). The fluorescent body 9 is formed by applying afluorescent body layer onto an aluminum substrate having a highreflectance, and the aluminum substrate reflects a fluorescent lightsubjected to fluorescence conversion from the blue color light towardthe condenser lens unit 8. The aluminum substrate reflects a part of theblue color light with the same wavelength without beingfluorescence-converted.

As described above, the white color light flux including the fluorescentlight including red color light and green color light and theunconverted blue color light is emitted from the fluorescent body 9, andcondensed and made into parallel light by the condenser lens unit 8. Theresultant light travels to an illumination optical system (notillustrated).

At this time, a case will be considered in which the width of thedichroic mirror 7, more specifically the width of the dichroic surface71, is sufficiently larger than the light flux diameter of the whitecolor light flux from the condenser lens unit 8. In such a case, theblue color light in the white color light flux passing through thedichroic surface 71 is reflected by the dichroic surface 71 and returnsto the side of the light source 1. The blue color light thus cannotpropagate to the illumination optical system.

More specifically, as the width of the dichroic surface 71 becomeslarger, attenuation of the blue color light increases. As means forsolving such attenuation of the blue color light, a configuration havinga blue color light source provided separately from the light source 1emitting excitation light may be considered as discussed in UnitedStates Patent Application Publication No. 2012/0133904, but thisconfiguration increases the size of the entire apparatus. Accordingly,to minimize the attenuated blue color light, minimizing the area of thedichroic mirror 7 is considered in the present exemplary embodiment.

More specifically, in the present exemplary embodiment, the width D_(d)of the dichroic surface 71 and the width D_(c) of the condenser lensunit 8 are configured to satisfy the following condition. Namely, thewidth D_(d) of the dichroic surface 71 is narrower than the width D_(c)of the condenser lens unit 8 in a direction perpendicular to the opticalaxis of the condenser lens unit 8 (Z axis direction) in a cross sectionparallel to the normal of the dichroic mirror 7 and including theoptical axis of the condenser lens unit 8 (XZ cross section).

In such a configuration, the blue color light which is in the whitecolor light flux from the condenser lens unit 8 and which is included inthe light flux passing through the dichroic surface 71 returns to theside of the light source 1, but the light flux not passing through thedichroic mirror 7 is guided to the illumination optical system withoutchange. In other words, even in a case where a blue color light sourceis not provided separately from the light source for the excitationlight and an optical system around the blue color light source is notprovided, the white color light flux can be guided to the illuminationoptical system, so that a smaller light source optical system can berealized.

In a case where the dichroic mirror 7 has the configuration asillustrated in FIG. 2A, the width of the dichroic mirror 7 in the Z axisdirection may be defined as D_(d). On the other hand, in a case of aconfiguration including the transmission surface 72 other than thedichroic surface 71 in the XZ cross section as illustrated in theconfiguration of FIG. 2B, the width of the dichroic surface 71 in the Zaxis direction may be defined as D_(d).

(Definition of Light Flux Diameter)

The width Dd being narrower than the width Dc can be paraphrased asfollows: a light flux diameter D_(LD) of the excitation light emittedfrom the micro lens array 63 is made smaller than the light fluxdiameter D_(phos) of the white color light flux from the condenser lensunit 8 by using the light flux diameter. The definition of the lightflux diameter referred to herein will be described with reference toFIGS. 4A and 4B.

FIG. 4A illustrates a luminance cross section diagram of a light sourceimage of excitation light formed on the second lens surface array 62. Asdescribed above, the light fluxes split on the first lens surface array61 are condensed on the second lens surface array 62, and an image of alight emission point of an LD is formed at the condensing point.

Accordingly, the luminance cross section diagram illustrated in FIG. 4Ahas a discrete distribution in which luminance peaks as many as thenumber corresponding to the lens cell pitch of the first lens surfacearray 61 are arranged. In this case, the light flux diameter D_(LD) ofthe excitation light from the micro lens array 63 is a half width athalf maximum of an envelope E of the luminance cross section, i.e., awidth where a luminance of ½ of the maximum luminance I is obtained.

On the other hand, FIG. 4B illustrates a luminance cross section diagramof a light distribution of a white color light flux from the condenserlens unit 8. While the fluorescent light from the fluorescent body 9 isemitted in all directions, the surface of the fluorescent body 9performs surface-emission, and therefore, this can also be understood asa perfect diffusion surface light source. Accordingly, in the luminancecross section of the fluorescence light flux, the luminance is thehighest near the optical axis, and the luminance decreases with anincrease in distance from the optical axis according to the cosine ofthe acceptance angle of the fluorescent light by the condenser lens unit8, but the luminance becomes zero at the limiting point of theacceptance angle that is determined by the effective diameter of thecondenser lens. In this case, the light flux diameter of the fluorescentlight, i.e., the light flux diameter D_(phos) of the white color lightflux from the condenser lens unit 8, corresponds to a width at theposition where the luminance is zero.

As described above, according to the configuration of the presentexemplary embodiment, the reduction in the size of the light sourceapparatus can be achieved while the reduction in the light conversionefficiency of the fluorescent body is suppressed.

(Problems Associated with Reduction in Size of Light Flux Diameter ofExcitation Light)

Now, a further reduction in the area of the dichroic mirror 7 tosuppress the attenuation of the blue color light caused by the largesize of the dichroic mirror 7 described above will be considered. In acase where the area of the dichroic mirror 7 is further reduced, it isnecessary to further reduce the light flux diameter of the excitationlight emitted from the second lens surface array 62. However, in a casewhere the light flux diameter of the excitation light is furtherreduced, the following problem arises. Hereinafter, the problem will bedescribed with reference to FIGS. 5A and 5B and FIG. 6.

FIGS. 5A and 5B illustrate the first and second lens surface arrays 61,62 according to the present exemplary embodiment in an enlarged scale.As illustrated in FIG. 5A, the parallel light fluxes split by the firstlens surface array 61 each are condensed on the corresponding lens cellof the second lens surface array 62 by each lens cell of the first lenssurface array 61. As a result, the light source image of the lightsource 1 is formed on each lens cell of the second lens surface array62.

If the size of the light source image is larger than the pitch of thelens cell, a part of the light flux may be incident upon a lens celladjacent to the corresponding lens cell. Such a component forms an imageat a position adjacent to a position of a predetermined light sourcespot on the fluorescent body 9, and such a component is rejected by anoptical element in an illumination optical system disposed at a latterstage, resulting in a light that is not effectively used, i.e., a loss.As a result, the light use efficiency is reduced.

FIG. 5B illustrates a case where the light flux diameter of theexcitation light is reduced to reduce the area of the dichroic mirror 7described above. In FIG. 5B, the light source image formed on each lenscell of the second lens surface array 62 is larger than the size of thelens cell, so that a light flux is incident upon a lens cell adjacent tothe corresponding lens cell described above, which further reduces thelight use efficiency. This is because the angle variation as theparallel light flux of the excitation light flux increases withreduction of the light flux diameter of the excitation light incidentupon the first lens surface array 61.

(Angle Variation of Light Flux Diameter of Excitation Light)

The principle thereof will be described with reference to FIG. 6. FIG. 6is a diagram illustrating a simplified optical relationship amongoptical elements from the light source 1 to the concave lens 5. A lightsource 1′ corresponds to the light source 1. Mirrors 2′ and 3′ areelements having positive powers and each correspond to a mirror of thecollimator lens 2 and the parabola mirror array 3, respectively. Aconcave lens 5′ is an element having a negative power, and is theconcave lens 5 as illustrated.

As described above, the parabola mirror array 3 and the concave lens 5share the focal point, and form an afocal system. Accordingly, theelements 3′ and 5′ corresponding thereto also form an afocal system A.The light emitted from the light source 1′ made into parallel light bythe collimator lens 2′ to be incident upon the afocal system A, and thelight flux is compressed at a predetermined magnification.

At this time, when the light emission point of the light source 1′ isinfinitely small, the light emitted from the light source 1′ iscompletely made into parallel light by the collimator lens 2′, but thelight emission point of the LD has a finite size, and accordingly, it ismade into a parallel light flux having an angle variation θ₁corresponding to the size thereof. The angle variation θ₁ is expressedas θ=a tan (L/f_(coli)) using a focal length f_(coli) of the collimatorlens 2′ and a size L of the light emission point.

As described above, the parallel light flux incident upon the afocalsystem A has an angle variation θ₁ corresponding to the finite size ofthe light emission point, but when the parallel light is incident uponthe afocal system A and the light flux diameter changes, the anglevariation changes to θ₂. Now, let D₁ and D₂ be the diameters of theparallel light fluxes before and after being incident upon the afocalsystem A, the following formula holds from the relationship of anangular magnification.

$\begin{matrix}{\frac{\tan\;\theta_{2}}{\tan\;\theta_{1}} = {\frac{D_{1}}{D_{2}}\mspace{14mu}\left( {= \gamma} \right)}} & {{Expression}\mspace{14mu}(1)}\end{matrix}$

Here, γ denotes the angular magnification. Further reducing the lightflux diameter of the excitation light incident upon the first lenssurface array 61 described above is equivalent to further reducing thelight flux diameter D₂ emitted from the afocal system A. When the lightflux diameter D2 is reduced, the angular magnification γ increases, andaccordingly, the numerical value of the left term increases, and as aresult, θ₂ increases.

Accordingly, when the diameter of the light flux emitted from the afocalsystem is reduced, the angle variation θ₂ increases, and in the latterstage thereof, the angle variation θ₂ of the parallel light fluxincident upon the first lens surface array 61 also increases. Then, asillustrated in FIG. 5B, the size of the light source image on the secondlens surface array 62 increases. More specifically, in a case where thelight flux diameter of the excitation light is reduced excessively byreducing the area of the dichroic mirror for the purpose of suppressingthe attenuation of the blue color light, the size of the light sourceimage formed on the second lens surface array 62 becomes larger than thepitch of the lens cell, and the light use efficiency decreases, which isnot desirable.

To that end, a reduction in the size of the light source spot formed onthe fluorescent body 9 will be considered. This means a reduction in thepitch of the lens cell of the first lens surface array 61 in theimage-forming relationship with the fluorescent body 9. When the pitchof the lens cell of the second lens surface array 62 is also reducedaccording to the reduction in the pitch of the lens cell of the firstlens surface array 61, the size of the light source image relativelyincreases with respect to the size of the lens cell. As a result, thelight use efficiency decreases, which is not desirable as in theaforementioned case.

(More Preferable Mode)

To obtain the configuration according to the present exemplaryembodiment while suppressing such loss, it is desirable that the lightflux diameter of the excitation light path and the size of the lightsource spot on the fluorescent body 9 satisfy the following condition.In the following description, a value obtained by dividing the focallength f_(c) of the condenser lens unit 8 by the light flux diameter isadopted as an F number, and the F number is substituted for the lightflux diameter. The reason for this is as follows.

The focal length of the condenser lens unit 8 according to the presentexemplary embodiment is f_(c)=15 mm, but the focal length of thecondenser lens unit 8 has a flexibility in design. Thus, in a case wherethe effective diameter of each optical element in the illuminationoptical system is large, the focal length is increased in proportionthereto, and the light flux diameter of the fluorescent light may beincreased while the acceptance angle is maintained. In this case, thelight flux diameter of the excitation light also changes in proportionto the focal length of the condenser lens, but the light flux diametercan be generalized by dividing each light flux diameter by the focallength of the condenser lens, which is desirable in terms ofcalculation.

When the light flux diameter of the white color light flux from thecondenser lens unit 8 according to the present exemplary embodiment isD_(phos)=30 mm, the F number to satisfy f_(c)=15 mm is as follows.

$\begin{matrix}{F = {\frac{f_{c}}{D_{phos}} = 0.5}} & {{Expression}\mspace{14mu}(2)}\end{matrix}$

Meanwhile, when the light flux diameter of the excitation light from themicro lens array 63 is D_(LD)=15 mm, the F number is as follows.

$\begin{matrix}{F = {\frac{f_{c}}{D_{LD}} = 1.0}} & {{Expression}\mspace{14mu}(3)}\end{matrix}$

In other words, according to the present exemplary embodiment, the Fnumber of the excitation light path, i.e., a light path in which theexcitation light is condensed on the fluorescent body 9, is larger thanthe F number of the fluorescent light path, i.e., a light path in whichthe fluorescent light is condensed by the condenser lens unit 8 asillustrated in FIG. 7A.

For example, a case where the F number of the fluorescent light path andthe F number of the excitation light path are substantially the samewill be considered. In this case, as illustrated in FIG. 7B, all or mostof the unconverted light from the condenser lens unit 8 is reflected bythe dichroic mirror 7 without being guided to the illumination opticalsystem, and accordingly, the loss increases, which is not desirable.Therefore, it is desirable that the relationship illustrated in FIG. 7Ais satisfied.

More desirably, when the F number of the fluorescent light path definedin the conditional expression (2) is defined as F_(phos), and the Fnumber of the excitation light path defined in the conditionalexpression (3) is denoted as F_(LD), the light source optical system cansatisfy the following expression.

$\begin{matrix}{0.4 < \frac{F_{phos}}{F_{LD}} < 0.6} & {{Expression}\mspace{14mu}(4)}\end{matrix}$

In a case where the lower limit value is less than that of theconditional expression (4), the F number F_(LD) of the excitation lightpath increases. In other words, the light flux diameter D_(LD) of theexcitation light is reduced. When the light flux diameter D_(LD) of theexcitation light is reduced excessively, the size of the light sourceimage formed on the second lens surface array described above becomeslarger than the pitch of the lens cell, and accordingly the light useefficiency decreases, which is not desirable.

On the other hand, in a case where the upper limit value is greater thanthat of the conditional expression (4), the F number F_(phos) of thefluorescent light path and the F number F_(LD) of the excitation lightpath are closer to each other. In this case, the loss increases asillustrated in FIG. 7B, which is not desirable.

In the present exemplary embodiment, eight LDs are made into a unit, andtotally four units are used, i.e., totally 32 LDs are used as a lightsource, and the light source spot formed on the fluorescent body 9 is ina substantially square shape, one side of which is about 1.0 to 1.5 mm.This is because when the light density of the light source spot on thefluorescent body 9 as described above increases, the light conversionefficiency is reduced due to the luminance saturation phenomenon, or thefluorescent body 9 is degraded in a shorter period of time.

For example, in case where the light source image on the fluorescentbody 9 is reduced, i.e., in a case where the pitch of the lens array isfurther reduced, the size of the light source image formed on the lenscell does not change, and the external shape of the corresponding lenscell becomes relatively smaller. As a result, the reduction in the lightuse efficiency occurs as described above, which is not desirable.

In a case where the F number of the excitation light path is defined asF_(LD), and the length of one side of the light source spot is definedas d_(phos) in view of the above relationship, it is desirable that thelight source optical system satisfies the following conditionalexpression.

$\begin{matrix}{1.0 < {\left\{ {\left( \frac{1}{F_{LD}} \right) \cdot d_{phos}} \right\}^{2}\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}} & {{Expression}\mspace{14mu}(5)}\end{matrix}$

The conditional expression (5) means that in a case where the F numberF_(LD) of the excitation light path is 1.0 as in the case of the presentexemplary embodiment, it is desirable that the area of the light sourcespot is larger than 1.0 mm². This is because problems occur, e.g., areduction in the light conversion efficiency due to the increase in thelight density of the light source spot on the fluorescent body 9 asdescribed above.

Furthermore, the conditional expression (5) means that in a case wherethe area of the light source spot is larger than 1.0 mm², the F numberF_(LD) of the excitation light path increases, i.e., the light fluxdiameter D_(LD) of the excitation light is reduced. With thisconfiguration, the area of the dichroic mirror 7 is reduced, so thatmore unconverted light can be guided from the condenser lens unit 8 tothe illumination optical system.

However, in a case where the light flux diameter D_(LD) of theexcitation light is excessively reduced, i.e., when the F number F_(LD)the excitation light path excessively increases, the lower limit valueis less than that of the conditional expression (5). In a case where thelight flux diameter D_(LD) of the excitation light is excessivelyreduced, the size of the light source image formed on the second lenssurface array 62 becomes larger than the pitch of the lens cell asdescribed above, and accordingly, the light use efficiency decreases,which is not desirable.

However, in a case where the area of the light source spot is too large,the performance as the point light source is decreased. Furthermore, ina case where the F number F_(LD) of the excitation light path is toosmall, i.e., when the light flux diameter D_(LD) of the excitation lightis too large, size of the dichroic mirror 7 increases, which makes itdifficult to guide the unconverted light from the condenser lens unit 8to the illumination optical system. Accordingly, it is further desirablethe light source optical system can satisfy the following conditionalexpression.

$\begin{matrix}{1.0 < \left\{ {\left( \frac{1}{F_{LD}} \right) \cdot d_{phos}} \right\}^{2} < {4.0\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}} & {{Expression}\mspace{14mu}\left( {5a} \right)}\end{matrix}$(Modification of Conditional Expression)

Here, the right-hand side of the conditional expression (5) is furthersimplified. The area of the light source spot can be expressed using acell pitch d_(LA) of a lens cell, a focal length f_(LA) of the lenscell, and a focal length f-_(c) of the condenser lens unit 8, and theright-hand side of the conditional expression (5) can be converted asfollows.

$\begin{matrix}{\left\{ {\left( \frac{1}{F} \right) \cdot d_{phos}} \right\}^{2} = {\left\{ {\left( \frac{D_{LD}}{f_{c}} \right) \cdot \left( {\frac{f_{c}}{f_{LA}}d_{LA}} \right)} \right\}^{2} = \left( \frac{D_{LD}d_{LA}}{f_{LA}} \right)^{2}}} & {{Expression}\mspace{14mu}(6)}\end{matrix}$

Here, the square of the light flux diameter D_(LD) of the excitationlight and the pitch d_(LA) of the lens cell at the right term of theexpression (6) is replaced with a cross section area S_(LD) of anexcitation light flux and an area S_(LA) of the lens cell as in theexpression (7).

$\begin{matrix}\left. \left( \frac{D_{LD}d_{LA}}{f_{LA}} \right)^{2}\rightarrow{S_{LD}\frac{S_{LA}}{f_{LA}^{2}}} \right. & {{Expression}\mspace{14mu}(7)}\end{matrix}$

Furthermore, the cross section area S_(LD) of the excitation light fluxcan be transformed as in the expression (8) by using the total number ofcells N of the lens cell and the area S_(LA) of the lens cell.

$\begin{matrix}\left. {S_{LD}\frac{S_{LA}}{f_{LA}^{2}}}\rightarrow{N \cdot S_{LA} \cdot \frac{S_{LA}}{f_{LA}^{2}}} \right. & {{Expression}\mspace{14mu}(8)}\end{matrix}$

Finally, the conditional expression (5) can be simplified only into theparameter of the lens cell as in the following conditional expression(9).

$\begin{matrix}{1.0 < {N \cdot S_{LA} \cdot {\frac{S_{LA}}{f_{LA}^{2}}\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}}} & {{Expression}\mspace{14mu}(9)}\end{matrix}$

In the present exemplary embodiment, the conditional expression (5) or(9) is satisfied, so that the size of the light source spot and the Fnumber F_(LD) of the excitation light, i.e., the light flux diameterD_(LD) of the excitation light, are set to an appropriate relationship.With this configuration, while the effect of the light density of thelight source spot on the fluorescent body 9 is suppressed, the increasein the size of the dichroic mirror 7 is suppressed, so that moreunconverted light can be guided from the condenser lens unit 8 to theillumination optical system. Furthermore, this configuration cansuppress the reduction in the light use efficiency, which is caused bythe light source image on the second lens surface array 62 increasingbecause of the light flux diameter D_(LD) of the excitation light beingexcessively reduced.

It is to be understood that it is more desirable that the light sourceoptical system satisfies the following expression, as in the case of theconditional expression (5).

$\begin{matrix}{1.0 < {N \cdot S_{LA} \cdot \frac{S_{LA}}{f_{LA}^{2}}} < {4.0\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}} & {{Expression}\mspace{14mu}\left( {9a} \right)}\end{matrix}$(Case of Fewer LDs)

In the present exemplary embodiment, 32 LDs are used in total asdescribed above, but fewer LDs may be used. In a case where eight LDsare made into a unit, and one unit (eight LDs in total) is used, theterm of SLD in the expressions (7) and (8) can be reduced to ¼, andtherefore, the lower limit value of the conditional expression (9) canbe alleviated as follows.

$\begin{matrix}{0.25 < {N \cdot S_{LA} \cdot {\frac{S_{LA}}{f_{LA}^{2}}\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}}} & {{Expression}\mspace{14mu}(10)}\end{matrix}$

More specifically, in a case where more LDs are used to increase thebrightness, it is desirable that the expression (9) is satisfied, but ina case where the number of LDs is small, at least the expression (10)should be satisfied. Accordingly, while this configuration can suppressthe occurrence of the loss that is caused when the light source imagebecomes larger with respect to the size of the lens cell, the reductionin the light conversion efficiency of the wavelength conversion elementcan be suppressed, and smaller light source optical system can berealized.

Furthermore, as in the conditional expression (5a) described above, itis desirable that the following expression is satisfied to suppress theeffect that is caused when the light source spot becomes larger.

$\begin{matrix}{0.25 < {N \cdot S_{LA} \cdot \frac{S_{LA}}{f_{LA}^{2}}} < {10\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}} & {{Expression}\mspace{14mu}\left( {10a} \right)}\end{matrix}$

Furthermore, is more desirable that the following expression can besatisfied.

$\begin{matrix}{0.25 < {N \cdot S_{LA} \cdot \frac{S_{LA}}{f_{LA}^{2}}} < {7.0\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}} & {{Expression}\mspace{14mu}\left( {10b} \right)}\end{matrix}$

As in the conditional expression (5a), the upper limit value of theconditional expression (10) may be set to 4.0.

Numerical Examples according to the present invention are as follows.

TABLE 1 Calculation results in conditional expression Numerical f_(c)D_(LD) D_(phos) d_(phos) S_(LA) f_(LA) (10) Examples [mm] [mm] F_(LD)[mm] F_(phos) F_(phos)/F_(LD) [mm] N [mm²] [mm] [mm²] 1 15.0 15.0 1.030.0 0.5 0.5 1.1 961 0.23 6.5 1.21 2 15.0 15.0 1.0 30.0 0.5 0.5 1.5 5290.42 6.5 2.24 3 15.0 15.0 1.0 30.0 0.5 0.5 1.0 1156 0.19 6.5 1.03 4 15.015.0 1.0 30.0 0.5 0.5 2.0 289 0.76 6.5 3.92 5 15.0 15.0 1.0 30.0 0.5 0.50.5 4624 0.05 6.5 0.26 6 15.0 29.0 0.5 30.0 0.5 1.0 1.0 4225 0.19 6.53.75 7 15.0 7.5 2.0 30.0 0.5 0.3 1.0 289 0.19 6.5 0.26

A second exemplary embodiment of the present invention will be describedbelow. FIG. 8 is a diagram illustrating a configuration of a lightsource apparatus according to the present exemplary embodiment. Thedifference between the first exemplary embodiment described above andthe present exemplary embodiment lies in the configuration of thedichroic mirror 7 and the position relationship of the condenser lensunit 8 and the fluorescent body 9 with respect to the dichroic mirror 7.

The dichroic mirror 7 according to the first exemplary embodimentdescribed above is configured to include the dichroic surface 71 havingcharacteristics that reflects the excitation light from the light source1 and allows the fluorescent light from the fluorescent body 9 totransmit therethrough and the transmission surface 72 allowing the lightto transmit therethrough regardless of the wavelength.

By contrast, a dichroic mirror 7 according to the present exemplaryembodiment is configured to include a dichroic surface 73 havingcharacteristics that allows excitation light from a light source 1 totransmit therethrough and reflects fluorescent light from a fluorescentbody 9 and a reflection surface 74 reflecting light regardless of thewavelength. In a case where the dichroic mirror 7 having such aconfiguration is used, the dichroic mirror 7, condenser lens unit 8, andthe fluorescent body 9 need to be arranged in the direction in which thelight flux from the light source 1 travels.

Even in such a configuration, the white color light flux can be guidedto the illumination optical system even if a blue color light source isnot provided separately from the light source for excitation light, anda small light source optical system can be realized. Furthermore, thereduction in the light conversion efficiency of the fluorescent body 9can be suppressed by the micro lens array 63.

A third exemplary embodiment of the present invention will be describedbelow. FIG. 9 is a diagram illustrating a configuration of a projector(projection display apparatus) having the light source optical systemand the light source apparatus according to the first exemplaryembodiment.

FIG. 9 illustrates a light source apparatus 100 according to the firstexemplary embodiment. The light source apparatus according to the secondexemplary embodiment may be used as the light source apparatus 100 inFIG. 9.

An illumination optical system 200 illuminates a liquid crystal panel 20(optical modulation element) described below by using a light flux fromthe light source apparatus 100. The illumination optical system 200includes a third fly-eye lens 13 a, a fourth fly-eye lens 13 b, apolarization conversion element 14, and a condenser lens 15.

The light flux from the light source apparatus 100 is split into aplurality of light fluxes by the third fly-eye lens 13 a, and forms alight source image between the fourth fly-eye lens 13 b and thepolarization conversion element 14. The polarization conversion element14 is configured to align the polarization direction of the incidentlight flux in a predetermined direction, and the light flux from thepolarization conversion element 14 is guided by the condenser lens 15 toa color separating/combining unit 300.

The color separating combining unit 300 includes a polarization plate16, a dichroic mirror 17, a wavelength selectivity phase differenceplate 18, a red color liquid crystal panel 20 r, a green color liquidcrystal panel 20 g, and a blue color liquid crystal panel 20 b. Theliquid crystal panels 20 r, 20 g, 20 b are collectively referred to as aliquid crystal panel 20. Furthermore, the color separating/combiningunit 300 includes a red color λ/4 plate 19 r, a green color λ/4 plate 19g, a blue color λ/4 plate 19 b, a first polarization beam splitter 21 a,a second polarization beam splitter 21 b, and a combining prism 22. Thered color λ/4 plate 19 r, the green color λ/4 plate 19 g, and the bluecolor λ/4 plate 19 b are collectively referred to as a λ/4 plate 19. Aportion of the color separating/combining unit 300 except for the liquidcrystal panel 20 is referred to as a color separating and combiningsystem.

The polarization plate 16 is a polarization plate that allows only thelight in the polarization direction aligned by the polarizationconversion element 14 to transmit therethrough, and the blue color lightand the red color light in the light from the polarization plate 16 isguided by the dichroic mirror 17 toward the second polarization beamsplitter 21 b. The green color light is guided toward the firstpolarization beam splitter 21 a.

The first polarization beam splitter 21 a and the second polarizationbeam splitter 21 b are configured to guide the light from the dichroicmirror 17 to the liquid crystal panel 20 according to the polarizationdirection, and guide the light from the liquid crystal panel 20 to thecombining prism 22. The λ/4 plate 19 gives a phase difference of λ/2 inthe reciprocation made by the reflection at the liquid crystal panel 20,so that the λ/4 plate 19 has an effect of enhancing the analysis effect.

The combining prism 22 combines the blue color light and the red colorlight from the second polarization beam splitter 21 b and the greencolor light from the first polarization beam splitter 21 a, and guidesthe combined light to a projection optical system 23.

According to such a configuration, the projector illustrated in FIG. 8can project a color image onto a projection surface such as a screen.

Furthermore, a positional relationship of the light source apparatus100, the illumination optical system 200, the color separating/combiningunit 300, and the projection optical system 23 with one another may notbe a relationship as illustrated in FIG. 8. More specifically, all ofthe optical axis of the condenser lens unit 8, the optical axis of thecondenser lens 15, a surface normal of the liquid crystal panel 20, andthe optical axis of the projection optical system 23 exist in the sameplane in FIG. 8. However, each axis does not necessarily exist in thesame plane, and may be changed as necessary so that the surface wherethey exist may be different depending on the axis by using a mirror andthe like.

The exemplary embodiments of the present invention have been hereinabovedescribed, but it is to be understood that the present invention is notlimited to these exemplary embodiments, and various modifications andchanges can be made within the gist thereof.

Other Embodiments

Each exemplary embodiment described above shows an example of aconfiguration in which the surface of the micro lens array 63 facing theconcave lens 5 is the first lens surface array 61, and a surface of themicro lens array 63 facing the side of the dichroic mirror 7 is thesecond lens surface array 62. Such a configuration can be used tosuppress a relative displacement between both the micro lens array 63and the first lens surface array 61.

However, the present invention is not limited to the aboveconfiguration. Instead of the micro lens array 63, a first fly-eye lenshaving the first lens surface array 61 and a second fly-eye lens havingthe second lens surface array 62 may be provided in that order from theside of the concave lens 5. In this case, the volume during glassformation can be reduced, so that it takes less time to form the glass.

Although the details have not been described in each of the exemplaryembodiments described above, the light source 1 and the collimator lens2 may be held by separate holding members, or may be held by the sameholding member. For example, an LD bank integrally including eight lightsources 1 and collimator lenses 2 may be used.

The light flux from the parabola mirror array 3 may be guided to theconcave lens 5 by using a prism instead of the flat mirror 4 accordingto each of the above embodiments.

In each of the above exemplary embodiments described above, for example,a light source image formed on the second lens surface array 62 by thefirst lens surface array 61. However, the light source image should onlybe formed near the second lens surface array 62. In other words, thelight source image may be formed between the second lens surface array62 and the fluorescent body 9, or between the second lens surface array62 and the dichroic mirror 7.

In each of the above exemplary embodiments described above, theconfiguration of the fluorescent body 9 made by applying a fluorescentbody layer onto a high reflectance aluminum substrate has beenillustrated as an example. More specifically, this may be aconfiguration in which a wheel made by continuously applying afluorescent body in a peripheral direction on a circular aluminumsubstrate may be rotated with a motor. According to such aconfiguration, the position where the laser light from the light source1 is condensed on the fluorescent body layer is changed, so that thedegradation of the fluorescent body layer can be suppressed.

In each of the above exemplary embodiments described above, for example,the dichroic surface 71 is provided as the light guide surface, but thepresent invention is not limited to such a configuration. For example,the light fluxes from multiple light sources 1 may be aligned in thepredetermined polarization direction, and instead of the dichroicsurface 71, a polarization dividing surface may be provided as the lightguide surface. The light fluxes from the fluorescent body 9 are emittedin such a state that the polarization directions are not organized, andaccordingly, on the polarization dividing surface, a light flux havingthe same wavelength as the light flux from the light source 1 can alsobe guided to the illumination optical system.

While the present invention has been described with reference exemplaryembodiments, it is to be understood that the invention is not limited tothe disclosed exemplary embodiments. The scope of the following claimsis to be accorded the broadest interpretation so as to encompass allsuch modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No.2015-232534, filed Nov. 28, 2015, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A light source optical system configured to guidea light flux from a light source to a wavelength conversion element, thelight source optical system comprising: a first lens surface arrayincluding a plurality of first lens surfaces; a second lens surfacearray including a plurality of second lens surfaces and configured toreceive a light flux from the first lens surface array; a condenseoptical system having a positive power and configured to guide a lightflux from the second lens surface array to the wavelength conversionelement; and a light guide surface configured to guide the light fluxfrom the second lens surface array to the wavelength conversion elementvia the condense optical system, wherein in a direction orthogonal to anoptical axis of the condense optical system in a cross section parallelto a normal of the light guide surface and including the optical axis ofthe condense optical system, a width of the light guide surface isnarrower than a width of the condense optical system, and the followingexpression is satisfied:${0.25 < {N \cdot S_{LA} \cdot {\frac{S_{LA}}{f_{LA}^{2}}\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}}},$where the number of the second lens surfaces is defined as N, a focallength of each of the respective second lens surfaces is defined asf_(LA), and an area of each of the respective second lens surfaces isdefined as S_(LA).
 2. The light source optical system according to claim1, wherein in a case where a value obtained by dividing a focal lengthof the condense optical system by a light flux diameter of a light fluxguided from the condense optical system to the light guide surface isadopted as an F number of a fluorescent light path, and a value obtainedby dividing the focal length of the condense optical system by a lightflux diameter of a light flux guided from the second lens surface arrayto the light guide surface is adopted as an F number of an excitationlight path, the F number of the excitation light path is larger than theF number of the fluorescent light path.
 3. The light source opticalsystem according to claim 2, wherein the following expression issatisfied: ${0.4 < \frac{F_{phos}}{F_{LD}} < 0.6},$ where the F numberof the fluorescent light path is defined as F_(phos), and the F numberof the excitation light path is defined as F_(LD).
 4. The light sourceoptical system according to claim 1 further comprising: a light guideelement including the light guide surface and a transmission surfaceconfigured to allow a light flux from the wavelength conversion elementto transmit therethrough regardless of a wavelength, wherein the lightguide surface is a dichroic surface configured to reflect a light fluxfrom the light source and guide the light flux to the wavelengthconversion element, and allow a light flux having a wavelength differentfrom that of the light flux from the light source among the light fluxfrom the wavelength conversion element to transmit therethrough in adirection different from the light source.
 5. The light source opticalsystem according to claim 1 further comprising: a light guide elementincluding the light guide surface and a reflection surface configured toreflect a light flux from the wavelength conversion element regardlessof a wavelength, wherein the light guide surface is a dichroic surfaceconfigured to allow the light flux from the light source to transmittherethrough and guide the light flux to the wavelength conversionelement, and reflect and guide, in a direction different from the lightsource, a light flux having a wavelength different from that of thelight flux from the light source among the light flux from thewavelength conversion element.
 6. A projection display apparatuscomprising: a light source; a positive lens provided in an advancingdirection of a light flux from the light source; a wavelength conversionelement; a light source optical system configured to guide the lightflux from the light source to the wavelength conversion element; anoptical modulation element; an illumination optical system configured toilluminate the optical modulation element by using a light flux from thelight source optical system; and a color separating and combining systemconfigured to guide the light flux from the light source optical systemto the optical modulation element, and guide a light flux from theoptical modulation element to a projection optical system, wherein thelight source optical system includes: a first lens surface arrayincluding a plurality of first lens surfaces; a second lens surfacearray including a plurality of second lens surfaces and configured toreceive a light flux from the first lens surface array; a condenseoptical system having a positive power and configured to guide a lightflux from the second lens surface array to the wavelength conversionelement; and a light guide surface configured to guide the light fluxfrom the second lens surface array to the wavelength conversion elementvia the condense optical system, wherein in a direction orthogonal to anoptical axis of the condense optical system in a cross section parallelto a normal of the light guide surface and including the optical axis ofthe condense optical system, a width of the light guide surface isnarrower than a width of the condense optical system, and the followingexpression is satisfied:${0.25 < {N \cdot S_{LA} \cdot {\frac{S_{LA}}{f_{LA}^{2}}\mspace{14mu}\left\lbrack {mm}^{2} \right\rbrack}}},$where the number of the second lens surfaces is defined as N, a focallength of each of the respective second lens surfaces is defined asf_(LA), and an area of each of the respective second lens surfaces isdefined as S_(LA).
 7. The projection display apparatus according toclaim 6, wherein in a case where a value obtained by dividing a focallength of the condense optical system by a light flux diameter of alight flux guided from the condense optical system to the light guidesurface is adopted as an F number of a fluorescent light path, and avalue obtained by dividing the focal length of the condense opticalsystem by a light flux diameter of a light flux guided from the secondlens surface array to the light guide surface is adopted as an F numberof an excitation light path, the F number of the excitation light pathis larger than the F number of the fluorescent light path.
 8. Theprojection display apparatus according to claim 7, wherein the followingexpression is satisfied: ${0.4 < \frac{F_{phos}}{F_{LD}} < 0.6},$ wherethe F number of the fluorescent light path is defined as F_(phos), andthe F number of the excitation light path is defined as F_(LD).
 9. Theprojection display apparatus according to claim 6, further comprising: alight guide element including the light guide surface and a transmissionsurface configured to allow a light flux from the wavelength conversionelement to transmit therethrough regardless of a wavelength, wherein thelight guide surface is a dichroic surface configured to reflect a lightflux from the light source and guide the light flux to the wavelengthconversion element, and allow a light flux having a wavelength differentfrom that of the light flux from the light source among the light fluxfrom the wavelength conversion element to transmit therethrough in adirection different from the light source.
 10. The projection displayapparatus according to claim 6, further comprising: a light guideelement including the light guide surface and a reflection surfaceconfigured to reflect a light flux from the wavelength conversionelement regardless of a wavelength, wherein the light guide surface is adichroic surface configured to allow the light flux from the lightsource to transmit therethrough and guide the light flux to thewavelength conversion element, and reflect and guide, in a directiondifferent from the light source, a light flux having a wavelengthdifferent from that of the light flux from the light source among thelight flux from the wavelength conversion element.